Isolate Mains Power to appliance as per TOPs P4
Close cold water inlet stopcock
Drain and discharge appliance
Close cold water inlet stopcock
Drain and discharge appliance
Observation:
Remove and inspect non return valve.
Refit non return valve after test.
Open cold water inlet stopcock and refill appliance.
Refit non return valve after test.
Open cold water inlet stopcock and refill appliance.
Isolate as per TOPs P4
and refit as necessary